1. Technical Field
The present invention relates to an electrophoretic display device, a method of driving the electrophoretic display device, and an electronic device.
2. Related Art
There is known an electrophoretic display device including, in pixels, control transistors, storage capacitors and driving transistors. See, for example, JP-A-2008-176330. In a pixel of such an electrophoretic display device disclosed in the document, a storage capacitor is charged by an image signal input through a control transistor, and a driving transistor supplies to a pixel electrode a current corresponding to the voltage of the storage capacitor. Thus, display with brightness in accordance with the amount of electric charge (current×time) is obtained.
In a pixel described in JP-A-2008-176330, a current Is that the driving transistor supplies is expressed by the following equation:
      I    s    =            1      2        ⁢          W      L        ⁢          C      ox        ⁢                  μ        ⁡                  (                                    V              g                        -                          V              s                        -                          V              th                                )                    2          where:    W is the channel width;    L is the channel length;    Cox is a constant represented by the expression ∈ox/tox (∈ox: the dielectric constant of a gate oxide film, tox: the thickness of a gate insulating film);    μ is the mobility;    Vth is the threshold voltage; and    Vg and Vs are the gate voltage and the source voltage, respectively.
In the above equation, W, L, Cox, μ and Vth vary from the transistor of one pixel to that of another. This leads to a variation in the current Is from one pixel to another, which causes differences in display gradation. Thus, display irregularities occur. Hereinafter, the product term (W/L)Coxμ in the above equation is collectively referred to as “mobility, etc.”